In his latest report, Ting Lu, China economist for Bank of
America-Merrill Lynch says he expects the official number to stay
above 51 in April. He also cites three key reasons for this
trend:

The HSBC index focuses more heavily on small-and-medium
enterprises (SMEs) than the official index. SME's could be hit
harder by tightened liquidity conditions, though liquidity
conditions have improved recently.

China’s export manufacturers tend to be of small scale, and
the HSBC PMI sample
could have more exposure to the export sector. Remember, export
growth decelerated to 7.6 percent YoY in the first quarter from
14.3 percent the previous quarter. In contrast, fixed asset
investment (FAI) and retail sales growth was strong in the first
quarter.

Finally, small manufacturers are less efficient and are being
consolidated into big ones which could affect the flash PMI
reading because of it's focus on SMEs.

Lu says it is misleading to judge the trend using just monthly
data and says the HSBC PMI tends to paint a more bearish picture
of China’s manufacturing sector at the moment than the official
number suggests. Moreover, he adds that the Chinese service
sector is quite resilient at this stage.

Lu expects a rebound in second quarter GDP growth to 8.5 percent,
from 8.1 percent in the first quarter.